postcss-unit-processor

postcss-unit-processor

PostCSS plugin to process css unit.

Install

$ npm install postcss postcss-unit-processor --save-dev

Usage

Use the processor function provided by the user to process the CSS unit. The default processor function is not to do any processing.

Example

var fs = require('fs');
var postcss = require('postcss');
var unitProcessor = require('postcss-unit-processor');
var css = fs.readFileSync('main.css', 'utf8');
var options = {
  processor: (value, unit) => {
    if (unit === 'px') {
      return value / 2;
    }
  }
};
var processedCss = postcss(unitProcessor(options)).process(css).css;

fs.writeFile('main-new.css', processedCss, function (err) {
  if (err) {
    throw err;
  }
  console.log('New file written.');
});

options

Type: Object | Null Default:

{
  processor: (value) => value,
  unitPrecision: 5,
  propList: ['*'],
  selectorBlackList: [],
  replace: true,
  mediaQuery: false,
  exclude: /node_modules/i,
  customUnitList: []
}

• processor (Function) css unit processing function.
  • The plugin will call this function when the conditions are met, and pass the following parameters:
    • value (Number): Unit value.
    • unit (String): The name of the unit.
    • node (Object): Current postCSS node object.
    • root (Object): postCSS node root object.
  • The function return value:
    • If the Number is returned, the unit value is directly replaced, and the unit name remains unchanged.
    • If an object is returned, the value of the object replaces the value, and the unit replaces the name.
• unitPrecision (Number) The decimal numbers to allow the processed units to grow to.
• propList (Array) The properties that can be changed by the processor function.
  • Values need to be exact matches.
  • Use wildcard * to enable all properties. Example: ['*']
  • Use * at the start or end of a word. (['*position*'] will match background-position-y)
  • Use ! to not match a property. Example: ['*', '!letter-spacing']
  • Combine the "not" prefix with the other prefixes. Example: ['*', '!font*']
• selectorBlackList (Array) The selectors to ignore.
  • If value is string, it checks to see if selector contains the string.
    • ['body'] will match .body-class
  • If value is regexp, it checks to see if the selector matches the regexp.
    • [/^body$/] will match body but not .body
• replace (Boolean) Replace rules instead of adding fallbacks.
• mediaQuery (Boolean) Allow processor function in media queries.
• exclude (String, Regexp, Function) The file path to ignore.
  • If value is string, it checks to see if file path contains the string.
    • 'exclude' will match \project\postcss-unit-processor\exclude\path
  • If value is regexp, it checks to see if file path matches the regexp.
    • /exclude/i will match \project\postcss-unit-processor\exclude\path
  • If value is function, you can use exclude function to return a true and the file will be ignored.
    • the callback will pass the file path as a parameter, it should returns a Boolean result.
    • function (file) { return file.indexOf('exclude') !== -1; }
• customUnitList (Array) List of custom units to process in addition to default units.
  • Values should be strings representing unit names (e.g., ['dp', 'rpx']).
  • Only non-empty strings containing letters and the percentage sign are accepted.
  • Custom units are added to the default set of units like px, rem, vw, etc.

Use with gulp-postcss and autoprefixer

var gulp = require('gulp');
var postcss = require('gulp-postcss');
var autoprefixer = require('autoprefixer');
var unitProcessor = require('postcss-unit-processor');

gulp.task('css', function () {

  var processors = [
    autoprefixer({
      browsers: 'last 1 version'
    }),
    unitProcessor({
      processor: (value, unit) => {
        if (unit === 'px') {
          return value / 2;
        }
      }
    })
  ];

  return gulp.src(['build/css/**/*.css'])
    .pipe(postcss(processors))
    .pipe(gulp.dest('build/css'));
});

Input/Output

// input
h1 {
  margin: 0 0 20px;
  font-size: 32px;
  line-height: 1.2;
  letter-spacing: 1px;
}
// output
h1 {
  margin: 0 0 10px;
  font-size: 16px;
  line-height: 1.2;
  letter-spacing: 0.5px;
}